On non-contrast CT, what does a hyperdense lesion most commonly represent?

• A. Air
• B. On non-contrast CT, a hyperdense lesion most commonly represents acute blood
• C. Calcified plaque
• D. Ischemic tissue

Answer: (B)

Hyperdensity on a non-contrast CT indicates something with high attenuation, most commonly acute blood. Fresh or clotted blood has a high iron/protein content that makes it stand out as a brighter (hyperdense) area compared with surrounding brain tissue. This is why an acute intracranial hemorrhage appears as a bright lesion on initial scans. Air appears dark, not bright. Ischemic tissue tends to be hypoattenuating (darker) early on due to edema, and calcifications can also be bright but are typically chronic and follow recognizable, non-acute patterns. So the bright, hyperdense finding is most often acute blood.